The present invention refers to a radio-receiving multiband antenna supported on window panes, particularly for a windshield of motor vehicles. The term "window pane" is intended to mean in this connection a pane of glass or of plastic material and the antenna may consist of electric conductors deposited by the silk screen process on the pane, preferably on that face of the pane which, when fitted into the car, is the internal one; or else, if in lieu of tempered glass, two bonded together glass panes are used, applied to that face of the pane, which is in contact with the other face. Obviously, in lieu of conductors made by the silk screen process, also a conducting metal wire may be used.
Obviously, such antenna may be applied to any window of a motor vehicle, although the windshield is the most suitable place.
The antenna according to the present invention has been designed to receive radio-frequency signals in their various bands of transmissions, such as long waves, medium waves, short waves, metric or frequency modulation waves (FM) and VHF, decimetric waves and UHF and all the waves for sound and/or television information, included the frequencies reserved for radio amateurs.
The antenna incorporated in the pane, particularly in the windshield, is preferred to the conventional, freely supported motorcar antennas, because they are subjected to various drawbacks, such as:
(a) considerable vibrations during driving which render the signal fluctuating, particularly when receiving distant stations and the receiver operates in threshold conditions;
(b) marked instability in their characteristics, such as increase of their resistance and consequent increase in their losses, changes in the capacity of the antenna, due to its aging, to the possibility of water penetration in the cylindric bottom element, which causes corrosion and oxidation of the tubular elements in a polluting or brackish atmosphere;
(c) in the case of fishpole antennas, the fact that they strongly project beyond the motorcar contours, which leads often to their breaking, for instance when entering a garage, an underpass, etc., or damaging persons and goods if they are badly installed;
(d) furthermore the fishpole antenna is also subject to be willfully broken by vandals.
For all these reasons windshield antennas have been developped.
It is well known that the major part of radio-receiving sets for motor vehicles is provided with a single aerial socket, differently from the domestic receivers which have an input for the medium waves and one for the metric waves (FM), therefore a problem which must be faced in the aerials embedded in motorcar windshields is that of obtaining good reception of the medium waves as well as of the metric waves in a single antenna socket of the radio-receiving set.
In the prior art various shapes of antennas incorporated or embedded in windshields have been suggested, in an attempt to ensure a good reception in all wave bands. For this purpose antennas have been devised having one central vertical fishpole-type straight or T-shaped element, which afford a good reception particularly in the field of metric waves, and have also been devised antenna elements of greater length which run along the rim of the glass pane, forming so-called "rim" conductors, which afford a good reception in the field of medium waves. However, the problem in these types of antennas with the distinct receiving elements in the various frequency bands is that the signals received by the individual elements conjoin correspondingly to the single input of the radio receiver, and thus it is difficult to obtain a good reception throughout all wave bands, since an antenna built for instance to give a good reception in medium waves is generally not fitted with the characteristics which may confer to it a good yield also in the reception of metric waves and vice versa. In the prior art there have been suggested types of antennas which were supported on the windshield of a motor vehicle, wherein that part of the antenna which was suitable for a certain frequency band, form an undesirable load when the antenna must operate for a different frequency band and furthermore, in particular in the reception of metric waves, these types of known antennas have a very variable efficiency in the various directions of reception.